Exposure apparatuses are commonly used to transfer images from a reticle onto a semiconductor wafer during semiconductor processing. A typical exposure apparatus includes an illumination source, a reticle stage assembly that retains a reticle, a lens assembly and a wafer stage assembly that retains a semiconductor wafer. The reticle stage assembly and the wafer stage assembly are supported above a mounting base with an apparatus frame.
Recently, in order to increase the throughput of the exposure apparatus, wafer stage assemblies have been developed that include two wafer stages. In this design, each wafer stage retains a wafer. Further, each wafer stage independently and alternately moves one of the wafers into an operational area for processing the wafers. Typically, the wafer stage assembly includes a wafer stage base and a wafer mover assembly that precisely positions the wafer stages relative to the wafer stage base.
The size of the images transferred onto the wafers from the reticle is extremely small. Accordingly, the precise positioning of the wafers and the reticle is critical to the manufacturing of high density, semiconductor wafers.
Unfortunately, the wafer mover assembly generates reaction forces that can vibrate the wafer stage base, the wafer stages, and the apparatus frame. The vibration influences the position of the wafer stage base, the wafer stages, and the wafers. This also reduces the accuracy of positioning of the wafers relative to the reticle and degrades the accuracy of the exposure apparatus.
In light of the above, there is a need for a stage assembly that precisely positions two devices independently in an operational area. Further, there is a need for a stage assembly having two stages that move independently and that minimizes the influence of the reaction forces of the mover assembly upon the position of the stages, the stage base, and the apparatus frame. Moreover, there is a need for an exposure apparatus capable of manufacturing precision devices such as high density, semiconductor wafers.